A revision of the fern genus Oleandra (Oleandraceae) in Asia

Abstract The Asiatic species of Oleandra (Oleandraceae) are revised. We reduce a large number of species to Oleandra neriiformis and Oleandra sibbaldii, we provide a revised circumscription of Oleandra cumingii and Oleandra undulata and we establish the identity of Oleandra vulpina. In total, we recognize 9 species, with full synonymy, descriptions and distribution maps. A list of identifications is appended.


Introduction
Virtually all authors who have dealt with the genus Oleandra Cav. have commented on its distinctness or naturalness. Th e shrubby growth form, particularly distinct in O. neriiformis Cav., prompted Cavanilles (1799; 1802) not only to derive the genus name, but also the species name from Nerium oleander L. (Apocynaceae). From this it should be clear that he saw the aerial stems of Oleandra neriiformis, of which the forms with distinctly whorled fronds are indeed strongly reminiscent of branches of Nerium oleander. Subsequently, Swartz (1801;1806) included Oleandra in Aspidium Sw., but Presl (1836) reinstated the genus, followed by Smith (1841;1842), and the distinctness of the genus has not been questioned since, not even by Hooker (1862), and only one author has preferred to recognize Oleandra at subgeneric level, but not without some doubts (Splitgerber 1840, "An genus proprium? habitus distinctissimus!"). Two genera have been described that are now universally included in Oleandra. Reinwardt (1825) described Ophiopteris Reinw., with the only species O. verticillata Reinw., without distinguishing either from Oleandra or O. neriiformis. Don (1825) distinguished Neuronia D. Don, with N. asplenioides D.Don as only species.
Th ere is as much unanimity on the distinctness of the genus as there is uncertainty on the distinctness of species in Oleandra, and many authors who have dealt with the genus have commented on the diffi culties of species delimitation. Smith et al. (2006) estimated a total number of c. 40 species, in which they follow many earlier authors, where the estimated number varies between 40 ("many species are similar in appearance", Kramer 1990) to 50 ("closely related", Pichi Sermolli 1965). However, Tryon (1997;2001) reduced the number of American species to 4 (with one species indicated as of doubtful validity: "it may well be a variety …") and of the Asiatic to 6. In addition, Pichi Sermolli (1965: "the delimitation of the species is not always easy, since some of them show a high degree of polymorphism"), distinguished no more than 5 species in Africa, and as his distinctions are sometimes subtle and based on limited material, the number should perhaps be reduced. A reasonable estimate of the number of species in Oleandra should accordingly be between 15 and 20. In this taxonomic treatment, we deal with the Asiatic species of Oleandra, extending the rather summary treatment in Tryon (2001), which was based on specimens in only two herbaria, and should be considered, according to the author, as "a prodromus that may be amplifi ed". After examining many more specimens in a much larger number of herbaria, we can only agree with Tryon and all others who have considered species delimitation in this group diffi cult.

Morphology
Much of the variability between species in Oleandra is found in the rhizome, but as large parts of the rhizome are usually not preserved in herbarium collections, it is difficult to appreciate and describe this variability without fi eld study. In the Asiatic species that we have seen, rhizomes may be relatively short-creeping, leading to more or less compact clumps of fronds, or more widely creeping. In the latter case, in some species the rhizome appears to be short-lived, decaying less than 1 m behind each growing point, which leads to stands with a scattered growth of plants. In others, the rhizome can be highly persistent, and stands may be extensive, with a dense growth of stems. In plants with this growth form, parts of the rhizome may also grow outwards or upwards from the substrate and form erect or drooping stems, here to be called "aerial" stems, that are often rootless. Branches are often opposite each other, and then both branches grow in the same direction, either downwards (positivel y geotropic) or upwards (negatively geotropic). Negatively geotropic branches can also be found on parts of the main rhizome where this starts to curve upwards, forming props that support the main stem. Th is is the shrubby growth form that is most often associated with the genus, although it occurs only in a minority of the species.
Th e anatomy shows a variably, but often very strongly developed peripheral sclerifi ed sheath, a ground tissue with or without scattered sclerenchyma strands, and a dictyostele. When aerial parts develop, they tend to be more strongly sclerifi ed.
Th e rhizome is covered with, usually persistent, rhizome scales with a peltate attachment. Th e scales are often strongly thickened near the attachment, and the margin can be nearly entire or densely set with woolly hairs (best visible in young scales) or sessile glands. Th e scales are strongly appressed or spreading to recurved -in the latter case the recurved parts tend to disappear on older rhizomes, giving the impression of a cover of short, appressed scales.
Roots arise mostly from the ventral side of the rhizome, and may be unbranched for a considerable length. Th e long unbranched parts have been described as rhizophores, but they were identifi ed as real roots by Wetter (1951). Branching and the formation of root hairs appears to be limited to the parts of the root that are in contact with a suitable substrate, and thus the unbranched parts tend to be more evident in species that creep over the substrate, often at some distance, or over dense cushions of moss, than in species with a subterraneous rhizome.
Fronds arise on the rhizome without any apparent regularity, sometimes clustered, sometimes more regularly spread over the length of a creeping rhizome. Th ey do not appear to grow in regular rows, but are inserted more or less dorsally on creeping stems, and often on all sides on aerial stems. At a variable position on the stipe, there is a distinct articulation point, where old fronds abscise cleanly, with a plane of dehiscence that is perpendicular to the stipe. Th e part below the abscission point might be called a phyllopodium, the part above it the stipe, but the upper part of the phyllopodium is in all structural details similar to the stipe, while basally it shows a gradual transition to the rhizome. A stipe-like phyllopodium like this is restricted, in ferns, to Oleandra and Arthropteris J. Sm., but in the latter genus, the articulation is distinctly much more oblique. In other ferns where fronds are articulated to the rhizome (Polypodiaceae, Davalliaceae), the part below the articulation is more clearly rhizomatous in structure and indument. In the most inclusive phylogenetic analyses available (Schuettpelz and Pryer 2007;Tsutsumi and Kato 2006), the optimization of the articulation of the fronds for the common ancestor of Oleandra and Arthropteris is ambiguous, so the homology of this type of articulation in Oleandra and Arthropteris is uncertain. Presence of an articulation in general (including the articulation of pinnae to the rachis) could well be an apomorphy for the crown clade of Eupolypods (Schuettpelz and Pryer 2007), related to the development of a climbing or epiphytic habit with a full reversal in the terrestrial Tectariaceae and a weaker reversal in the similarly terrestrial Cyclopeltis J.Sm.
Th e lamina is uniformly simple in all species, and varies little in shape, except in O. werneri Rosenst.¸ which is dimorphic, with the fertile fronds or parts of fronds strongly contracted. Sori are indusiate with a reniform indusium, and always separate. Th e indusia may be fi rm and persistent or shriveling and inconspicuous in older sori. Th e sori are borne dorsally and singly on the veins, at distances from the costa that vary strongly. Sporangia are long-stalked, often with a number of glandular hairs attached to the distal part of the stalk, just below the capsule. Th e capsule is of the common Polypodiales type.

Figs 1-10
Th e morphology of the spores of Oleandra as shown with SEM has been illustrated by Liew (1977) and Tryon and Lugardon (1991), who illustrate the whole range of variability in perispore morphology in Oleandra.
Two distinct types of perispore morphology can be distinguished. Th e fi rst type occurs in all species studied except O. wallichii. It is highly variable but the variation can be described in terms of just three parameters describing the folds, the ornamentation of the surface and the degree of perforation. Th is type shows a surface with a pattern of coarse folds, a variable ornamentation and a variable degree of perforation ("lophate", Liew 1977). Th e folds may be broad (fi g. 1), narrow (fi g. 2), or replaced by fi ssures (fi g. 3), the ornamentation ranges from warty (fi g 1) to densely spinose (fi g. 2, 4). Th is surface may be perforated (fi g. 4) or fi ssured to varying degrees, exposing an inner structure of numerous narrow cylindrical pillars c. 0.5 μm thick (fi g. 7). Th ese pillars are attached to a thin basal layer that adheres closely to the exospore. In the extreme case, the outer surface is so strongly perforated that the entire perispore consists of an open mesh (fi g. 4). Within this range of variability, most species that could be studied with an adequate sample of specimens show variability in two or more of these parameters, and it is diffi cult either to subdivide this type or to identify character states that are characteristic for one species, although it appears that O. sibbaldii has a more consistently highly perforated perispore than the other species.
Th e second type occurs exclusively in O. wallichii (fi gs 5, 6, 8). Here the perispore is composed of a thicker basal layer and thicker, more conical spines (fi g. 8) with a basal diameter of 1-2 μm, which are, mainly in the specimens from Taiwan, partly fused in irregular ridges (fi g. 7). In this type there never is an outer layer overlaying this pattern of conical spines, and thus the entire perispore is massive.
Th e exospore is smooth in all cases where it has been observed. Spore size variability was assessed based on SEM observations, with length of the spore measured including the perispore (Table 1, fi g.9). Th e limited data available do not allow a full statistical analysis, but it is clear that several species and even several specimens show a large variability in spore size. A similar variability in Oleandra from Southern Africa was found by Harmata and Kornas (1978).

Karyology
Data on chromosome numbers for species of Oleandra were summarized by Löve et al. (1977), who cite a basic number of x=41. Reports of n=40 (Kramer 1990) are based on a count that is acknowledged as uncertain by the authors (Manton and Sledge 1954) and that has not been confi rmed by others.
Of the Asiatic species, O. neriiformis (1 count, source Himalayas), O. musifolia (Bl.) C. Presl (2 counts, Ceylon and Southern India) and O. wallichii (Hook.) C. Presl (2 counts, Northern India) have been reported. Th e report of a tetraploid taxon in Oleandra is based on a count for unsourced material growing in Kew (presumably from Africa), and is complemented by reports of n=41 for another plant from West Tropical Africa. Th e large variation in spore size in Oleandra from Southern Africa was conjectured by Harmata and Kornas (1978) as due to the presence of diff erent polyploidy levels, and this explanation would also fi t well with the observed variability in morphology of Oleandra in Asia. However, actual confi rmation of polyploidy in O. neriiformis or any other Asiatic species is needed.

Systematics
Th e simple morphology of Oleandra has made comparison with other ferns diffi cult, and its position has been judged to be with Dryopteridaceae or Davalliaceae, where it has been associated in particular with Nephrolepis Schott and Arthropteris (Copeland 1947, Holttum 1959, Nayar and Bajpai 1978. More recent views exclude Nephrolepis from this alliance (Kramer 1990, Tryon and Lugardon 1991, Tryon and Tryon 1982, and phylogenetic molecular studies (Kuo et al. 2011, Schuettpelz andPryer 2007) have shown that these three genera do not form a clade, but that they are associated with diff erent clades in the crown leptosporangiates.

Taxonomic revision
Th is study is based on material from B, BISH, BM, BO, K, KEP, KLU, L, P, PE, PNH, MICH, SING, UC (abbreviations follow Index Herbariorum, Th iers 2011). All specimens cited were seen except where noted otherwise. Specimens seen only as on-line images (provided either directly through the database of the holding institute or via JSTOR, http://plants.jstor.org) are marked with *. Th e identifi cation list (see Appendix 1) has been prepared with the help of BRAHMS (http://dps.plants.ox.ac.uk/bol/BRAHMS), and the distribution data with BRAHMS and DIVA-GIS (http://www.diva-gis.org/). Description. Terrestrial, epilithic or epiphytic, creeping or scrambling ferns. Rhizome scaly, roots scattered, often with long rhizophore-like proximal parts, fronds scattered or in whorls, on stipe-like phyllopodia, dehiscing at a slightly thickened articulation point. Fronds stipitate, lamina simple, margin entire, veins distinct, somewhat raised on both sides, 1-2 ´ forked at or near the costa, costa often with narrow scales, lamina and veins often with acicular or capitate hairs. Sori in one, often irregular row on each side of the costa, with a more or less reniform, glabrous or hairy indusium. Sporangia stalked, stalk often with a number of sessile or stalked glands below the sporangium, sporangium body glabrous, spores monolete, perispore with broad wings, sometimes highly perforate, or echinate, massive.
Key to the 9 Asian species Description. Rhizome with creeping parts unknown, aerial stems unbranched and rootless, 2-3 mm thick (when dry), not white waxy, in cross-section with a distinct sclerifi ed peripheral sheath and few, scattered sclerifi ed strands, phyllopodia in weak to distinct clusters of 4-6, short, usually less than 5 mm long. Scales persistently covering the rhizome, peltate, 5-70 × 0.5-1 mm, appressed (sometimes spreading), dark, shining with pale to brown margin and acumen, margin ciliate especially when young. Fronds monomorphic; stipe 1-1.5 cm long, without dark colouration, with up to 1 mm long glandular hairs and often small, appressed scales; lamina 13-30 × 1.2-3.3 cm, linear, base narrowly cuneate to rounded, apex acuminate to caudate with cauda to 1.5 cm, texture coriaceous; costa and veins on lower surface densely hairy with up to 1 mm long, acicular hairs, costa without dark colouration, with copious, conspicuous, 3-4 mm long pale to brown scales, upper surface more glabrous, mostly hairy on the costa only, with similar hairs and with less copious scales. Sori in a single more or less irregular medial row, separated from the costa by a 2-7 mm wide sterile zone,  indusium distinct, c. 1.5 mm wide, most often glandular. Sporangial stalk with glands below the sporangium. Spores with coarse confl uent ridges, areolae with short pointed excrescences, perispore hollow, with internal baculae, outer layer distinctly perforated. Distribution. Brunei, Indonesia: Kalimantan Timur; Malaysia: Sarawak. E cology. Terrestrial in montane forest, mainly on ridges and in summit vegetation, 1100-2200 m.
Discussion. Creeping and rooting parts of the rhizome are absent in all collections seen, but presumably present, as in O. neriiformis. Th e lamina of O. coriacea is indeed much more coriaceous than O. neriiformis, and has copious large pale costal scales and long hairs especially on lower surface. Th e sori are consistently medial, with fi rm indusia that are often clearly glandular on their surface. Description. Rhizome short-to long creeping, 3-8 mm thick, sometimes white waxy in the older parts, little branched and not forming extensive stands, in crosssection with or without scattered sclerifi ed strands; roots scattered, sometimes with unbranched aerial parts; phyllopodia scattered or more or less tufted, (1-)3-10 cm long. Scales persistently covering the rhizome, peltate, 4-9 × 0.5-1.5 mm, appressed, acumen with dark center and lighter acumen and margin, margin ciliate especially when young. Fronds monomorphic, stipe 2-12 cm long, without dark colouration, glabrous or hairy with catenate to acicular up to 2 mm long hairs, lamina 12-40 × 2-4.5 cm, base narrowly cuneate to truncate, apex acute to long-acuminate, texture thin-chartaceous, both surfaces and margin with catenate or acicular hairs 0.2-1 mm long, usually more densely on lower surface, costa without dark colouration, on lower surface without or with few, pale to dark scales. Sori close to or scattered up to 2 mm from the costa, indusium distinct, 1-2 mm wide, densely hairy with short or long hairs. Sporangial stalk with glands below the sporangium. Spores with broad or narrow confl uent ridges, surface variably ornamented with small pustules to narrow spines, perispore hollow, with internal baculae, outer layer not or fi nely perforated, sometimes fi ssured along the ridges. Distribution. China: Yunnan, Guangdong, Guangxi, Guizhou; Laos; Th ailand (Peninsular); Malaysia: Peninsular Malaysia; Indonesia: Flores; Timor Leste; Philippines: Luzon.

Oleandra cumingii
Ecology. Terrestrial or on rocks, cliff s and roadsides in open forest, sea level to c. 1200 m.
Discussion. Contrary to Holttum (1968a), Oleandra cumingii J. Sm. is not a nomen nudum, but provided with an adequate diagnosis. Cuming 60 is distributed in several herbaria with many duplicates, and it is impossible to tell which ones should be considered isotypes of O. cumingii and which ones of O. macrocarpa.
Oleandra cumingii is a variable assemblage of fairly widely scattered forms, in many characters intermediate between O. undulata and O. musifolia. From O. undulata it can be distinguished by the more narrowly elongated, appressed rhizome scales with a more or less thickened costa in the acumen, and by the often hairy upper surface of the lamina. From O. musifolia, O. cumingii diff ers in the elongated phyllopodia and the distinctly tomentose indusia and lower surface of the lamina. Th e diff erences with either species, however, are often slight and bridged by specimens with an intermediate character combination. Th is may indicate that Oleandra cumingii is a hybrid or a hybrid swarm between the two other species, but failing positive evidence for that interpretation, we prefer to regard it here as a separate species. Description. Rhizome creeping, 5-8 mm thick, white waxy in the older parts, often supported above the substrate by unbranched stilt-like roots, dorsiventrally fl attened, (strongly compressed, 4-6 mm wide when dry), with up to 10 cm long, curved internodes (only occasionally straight and then often much longer) terminating in a cluster of a few short phyllopodia, usually less than 5 (-15) mm long, often hidden by the scales, rhizome often innovating just below this cluster, lateral branches usually basal on the internodes, in opposite pairs; all parts in cross-section without or with few sclerifi ed strands, roots scattered, with long unbranched aerial parts. Scales persistently covering the rhizome, peltate, 5-10 × 1-1.5 mm, appressed, with dark center and lighter brown acumen and margin, margin ciliate especially when young and with sessile glands. Fronds monomorphic, stipe 0.5-4 cm long, without dark colouration, with short, glandular hairs; lamina to 60 × 4.2 cm, linear, base cuneate to truncate or more or less rounded, apex acute to long-acuminate, texture thin-chartaceous, both surfaces with catenate, often glandular hairs 0.2-0.5 mm long; costa without dark colouration, on lower surface with inconspicuous, 1-3 mm long brown scales. Sori mostly in a single regular row close to the costa, sometimes more scattered over a 2-5 mm wide zone close to the costa or at a distance of up to 3 mm, indusium distinct, 1.5-2 mm wide, glabrous or glandular, sometimes setose. Sporangial stalk with glands below the sporangium. Spores with coarse confl uent ridges, areolae with short pointed excrescences, perispore hollow, with internal baculae, outer layer not or hardly perforated.
Ecology. Mostly terrestrial or on rocks, less often as low trunk epiphyte, in various types of forests, often disturbed, sea level to c. 2000 m.
Discussion. ICN 60.8 specifi es that the spelling of the original epithet "musaefolia" should be corrected to "musifolia".
Aspidium moritzii is one of the two species distinguished by Kunze (1848) among the collections under Zollinger 1306 (see also discussion under Oleandra neriiformis). Th e description conforms to O. musifolia, and the specimen selected as lectotype for Aspidium moritzii is conform to the original description, and bears a label "Aspidium moritzi 1306B". Aspidium lomatopus is based on a description and name in Kunze (1848) that was evidently considered preliminary by Kunze, as he did not refer to this species in his later account (Kunze 1851). A specimen in K is labeled "Zollinger 1306 b Aspidium moritzii Kze", with a separate label "Oleandra lomatopus" in what may be Kunze's hand. It is O. musifolia, and is here selected as lectotype.
Oleandra musifolia is variable in the density of hairs is variable, and the distance of the sori to the costa. It can be distinguished from O. cumingii mainly by the short phyllopodia (longer in O. cumingii). Incomplete collections are easily confused also with O. neriiformis but can often be recognized by the fl atter, softer rhizome without sclerenchyma strands (rhizome more rigid, rounded, with sclerenchyma strands in O. neriiformis) and by the catenate hairs with capitate or glandular apex (more acicular, not capitate in O. neriiformis). Distinguishing these two species on basis of juvenile material, however, is diffi cult, and often impossible. Description. Rhizome with main st ems creeping or ascending, 3-8 mm thick, white waxy in the older parts, creeping parts sparsely rooting, branches often in opposite pairs, ascending parts rootless, at base propped up by downwards directed branches, ultimately aerial, erect or pendent; branches single or in opposite pairs, mostly directly above a frond cluster, all parts in cross-section with a peripheral sclerifi ed sheath and scattered sclerifi ed strands, phyllopodia on creeping parts few, scattered, on aerial parts in more or less dense, often whorled clusters and branches, short to 15 mm long. Scales persistently covering the rhizome, peltate, 4-6.5 × 1-1.5 mm, appressed to squarrose, with dark center and lighter margin and acumen, margin ciliate. Fronds monomorphic or weakly dimorphic, stipe short to 3.5 cm long, without dark colouration; fertile lamina 12-43 × 0.5-4.5 cm, base gradually narrowed to narrowly truncate, then often somewhat lyrate, apex acuminate or to c. 2 cm caudate; sterile, if present, usually slightly shorter and wider, to 36 × 5.5 cm; texture thin-chartaceous, costa and lamina on lower surface without dark colouration, glabrous or with up to 2 mm long hairs, costa often with up to 2 mm pale to dark narrow scales. Sori in a single row close to the costa, or more scattered over a 2-5 mm wide zone close to or at a distance of up to 4 mm from the costa, indusium inconspicuous to distinct, to c 1.5 mm wide, glabrous to hairy. Sporangial stalk with glands below the sporangium. Spores with coarse confl uent ridges, surface pustulose or with pointed excrescences, outer layer variably perforated. Distribution. India (Himalayas), China (Xizang), Malesian archipelago to Australia, Pacifi c Islands (Fiji, Samoa).

Oleandra neriiformis
Ecology. Terrestrial or epiphytic, in various types of forests, in open places, often making up a signifi cant part of summit or ridge scrub. Sea level to 2200 m.

Discussion.
Th e epithet neriformis published by Cavanilles has to be corrected to "neriiformis" (ICBN 60.8). Th e epithet neriifolia used by Presl is either a mistake to be corrected or a superfl uous nom. nov. and should not be used.
Oleandra neriiformis does not occur in Australia. Th e reference in Bell (1998) to O. neriiformis refers indeed to O. musifolia as suggested.
Oleandra maquilingensis is based on two sterile specimens that are considered to represent juvenile plants by Price (1974). Price selected, but did not publish, a lectotype from among the two, and we here follow that lectotypifi cation. Th e identifi cation of these sterile specimens with O. neriiformis rather than O. cumingii is somewhat conjectural, as is the identifi cation of Blechnum colubrinum Blanco, for which no specimens at all are available.
Aspidium phyllarthron is one of the two species distinguished by Kunze (1848) among the specimens distributed as Zollinger 1306. In addition, Kunze cited Zollinger 1957. We have not found any specimens of Zollinger 1957, and from the several specimens that have been distributed as Zollinger 1306, we have selected one that fi ts the description of Aspidium phyllarthron and has a label "1306=1957". Another specimen, labeled "Zollinger 1306 a, Aspidium phyllarthron" (L 0317412), does not fi t the description and is O. musifolia.
Variability. With its wide-creeping and persistent rhizome, Oleandra neriiformis may form extensive and probably long-lived stands, which, especially when it is collected a number of times over a long period, may give the impression of the presence of a locally abundant species with a highly constant and distinct combination of characters. We expect this is at least partly the basis for the multitude of local species that have been described, and that we all include in O. neriiformis. Another problem is posed by the occurrence of juvenile plants in which the rhizome is not characteristically developed, and which may have much more softly hairy fronds than well-developed plants, blurring the distinctions to O. musifolia and O. cumingii.  Th e following characters or character complexes, some of which have been used to distinguish species, are variable in particular: 1 Place of the stipe articulation. Th e phyllopodium may be distinctly longer than the very short stipe (fi g. 12 k, n), or a distinctly elongated stipe may be present equal to or longer than the phyllopodium (fi g. 12 a, d) 2 Length and density of lamina hairs. Although the presence or length of lamina hairs is usually highly variable, some forms have constantly and distinctly longer hairs. 3 Location of soral zone. Sori may be located in a narrow zone close to the costa (fi g. 12 b, n), or in a more irregular zone at some distance from the costa (fi g. 11 b, m). 4 Indusium. Th e presence of an indusium is rarely constant over an area. It may vary from distinct and often fi rm (fi g. 11 h, 12 b) to inconspicuous (then often hairy) or absent (fi g. 11 a, k). 5 Costal scales: Some forms have uniformly pale and fl at costal scales, some have almost uniformly narrow, dark scales, and there are forms that vary in this character.

Geographic variation and local forms.
Over most of the distribution area, two forms can often easily be distinguished locally, on basis of the relative length of phyllopodium and stipe. Stipitate forms have short phyllopodia, elongated stipes (thus the articulation is positioned at the base of the phyllopodium/stipe), the lamina gradually narrowed towards the base, and sori relatively close to the costa (fi g. 12 k-m). Th is corresponds to the type of O. neriiformis. Th e other form is characterized by longer phyllopodia, stipes short or absent (thus the lamina appearing sessile with regard to the articulation, fi g. 2 b), usually a truncate lamina base (although the lamina directly above the base may be strongly narrowed, the base is still suddenly contracted, and often somewhat lyrate, fi g. 2 c) that is clearly set off against the stipe, and sori in a more variable position, in some cases almost at the margin (fi g. 2b). Other characters, such as indument, or indusium are independently variable and often vary in a similar way across the two forms where they co-occur, thus giving rise to diff erent characteristic character combination in diff erent parts of the distribution area.
Continental Asia. Th e few collections from continental Asia do not allow for an evaluation of the variability. Java, Sumatra. On Java and Sumatra, there is no distinction between stipitate and sessile forms, as both stipe and phyllopodium lengths are strongly variable and extremes are not sharply separated. In Backer and Posthumus (1939), all are taken together as O. neriiformis. Description (see also fi g. 12 h-j): Phyllopodia 2-6 mm, stipes 3-10 mm, lamina base narrowed, never lyrate, lamina variably hairy (mostly glabrous), costal scales usually few, medium dark; sori costal or at short distance from the costa, indusia distinct to fi rm, glabrous. Peninsular Malaysia, Southern Th ailand. In collections from the Malay Peninsula the diff erence between stipitate and sessile forms is associated with diff erences in hairiness of the lamina and position of the sori. Holttum (1968b) also distinguishes these two forms, on basis of the same characters, but notes that that they are not sharply distinct, nor ecologically sharply separated, although he cites a diff erence in elevational specifi city. Th e scant label data indicate no diff erences in specifi city for epiphytism vs terrestrial, or for elevation. Stipitate form description: Phyllopodia very short, stipes elongated, c. 5-10 mm long, lamina glabrous, occasionally hairy, margin glabrous or very nearly so, sori subcostal in an irregular row. Sessile form description (see also fi g. 12 k-n): Phyllopodia elongated, 1-6 mm long, stipes mostly very short, sometimes to 3 mm long, lamina hairy, sori strictly costal (rarely to 1 mm from costa).
Borneo. On Borneo, the two forms also diff er in hairiness of lamina, but not in the position of the sori, which is usually more or less closely costal. Here, the stipitate form is almost exclusively reported as epiphyte, the other form as terrestrial. Both forms tend to have narrower, darker costa-scales than in other areas. Completely glabrous forms such as are most common on Java and Sumatra are not found on Borneo. Th e sessile form has been described as O. oblanceolata Copel. Stipitate form description: Phyllopodia up to 6 mm long, stipe 7-25 mm, lamina at base gradually narrowed, usually hairy with relatively long hairs (rarely glabrous), costal scales more or less frequent, mostly brown. Almost exclusively reported as epiphyte. Sessile form description (see also fi g. 11 g-j): Phyllopodia 2-8 mm long, stipes at most 1 mm, lamina at base truncate, often ± lyrate, lamina mostly glabrous, sometimes short-hairy, costal scales not frequent, dark, narrow. Mostly reported as terrestrial.
Philippines. On the Philippines, distinctly stipitate forms represent a small minority of all collections (e.g., Cuming 94,Soejarto 8874,PNH 3862,8710), but include the type of Oleandra neriiformis (Christensen 1937). Th e two forms here do not show any diff erence in degree of hairiness and position of the sori, but share a distinctly hairy lamina and more copious, pale, fl at rachis-scales than the forms in other areas. Copeland (1958) distinguishes O. neriiformis from the short-stipitate form, and within the latter a number of species, based on details of indument: O. herrei, with paleate costa, O. colubrina, with setose costa and lamina, O. nitida, with setose costa and glabrescent lamina. We fi nd that although the density of costal scales varies strongly (it seems to be negatively and weakly correlated with the density of setae), scales can be found on all specimens, and the density of hairs on the lamina varies strongly. We see no basis on which these characters could lead to the distinction of clear groups.
Stipitate form description: Phyllopodia to 2 mm, stipes to c. 7 mm, lamina and margin hairy with highly variable density, costa mostly with many pale scales, sori not closely costal to medial or submarginal, indusia glabrous, often small, indistinct. Sessile form description (fi g. 11 k-m): Phyllopodia 5-15 mm, stipes short, up to 1 mm long, otherwise similar.
Celebes, Moluccas. In eastern Malesia south of the Philippines, two forms cooccur on Celebes and the Moluccas, while the stipitate form extends to the Solomon islands and Vanuatu. Both forms here have indusia that are frequently shortly setose.
Sessile form description: Phyllopodia 5-15 mm, stipes very short to occasionally 3 mm long, lamina base narrowed to ultimately cuneate, not distinctly lyrate, lamina indument often long, conspicuous on all veins, margin often distinctly fi mbriate with hairs similar to these on the lamina, costal scales few or absent, dark, sori narrowly costal, indusium distinct and persistent but not fi rm, often with narrow sinus, sometimes setose. Kato (1989) distinguishes the specimens from Ceram with a very small, setose indusium as O. cuspidata, but this represents only the extreme state of variability.
Fiji, Samoa. More eastwards in the Pacifi c Islands, there is no variability in the location of the articulation. All specimens from this area have elongated stipes, and can collectively be distinguished from the forms in other areas by the distinctly more lax clusters of fronds on the aerial stems (fi g. 12 a), with the fronds mostly hardly clustered at all (a character in which they resemble O. pilosa Hooker, from Tropical America). Regional diff erences show up mainly in the indument of the fronds. On Samoa, the lamina is less densely hairy than on Fiji, and the hairs on the lamina, when present, are distinctly shorter than those on the margin. Costa scales also diff er, and are distinctly darker on Samoa than on Fiji, while sori are somewhat less strictly costal on Samoa.
New Guinea and surrounding islands. Th e stipitate form that extends eastwards from Celebes co-occurs, on the main island of New Guinea, with a sessile form that is often distinctly dimorphic and has sori often quite distant from the costa.
Sessile form description (see also fi g. 11 a-c): Phyllopodia to 4 mm, stipes very short or absent, articulation directly below the base of the lamina, fronds slightly but usually distinctly dimorphic, lamina narrowed to a truncate or somewhat lyrate base, costal scales mostly brown to dark, lamina glabrous or sometimes short setose, with hairs to 0.5 mm long, margin usually with a few scattered pale, acicular hairs especially near the base, sori medial or submarginal leaving a sterile zone of 0.5-7 mm wide, indusia small and inconspicuous in older sori, occasionally more distinct, often fringed with pale acicular hairs. Description. Rhizome long-creeping or pendulous, sparsely branching, 1.5-4.5 mm thick, very strongly white waxy, in cross-section without or with few scattered sclerifi ed strands, phyllopodia scattered, (0.3-)0.8-4.0(-5.7) cm long, roots with distinct unbranched parts. Scales deciduous, exposing the rhizome in older parts, peltate, (3-)5-15(-18) × (0.3-)0.4-0.9(-1.2) mm, usually widest above the attachment, squarrose, reddish brown, margin entire or more or less densely set with sessile glands, acumen attenuated, long fi liform apex. Fronds monomorphic; stipe (0.3-)0.5-3.5(-4.5) cm long, often with dark coloration on abaxial side; lamina to (4.5-)15-40(-58) × 1-4(-6) cm, widest in middle part, base attenuate to cuneate, sometimes rounded, rarely truncate, sometimes asymmetric, apex acuminate or up to 3 cm caudate, texture membranous to coriaceous, both sides sparsely to densely set with catenate hairs to c. 0.5 mm long; costa on lower surface often with dark-coloration, on both surfaces with scales, scales on lower surface often abundant, to 6(-11) × 1(-1.2) mm, pale to dark brown, on upper surface scarce, inconspicuous. Sori inframedial, leaving a distinct 1-4 mm wide sterile zone between costa and soral zone, sometimes as much as 12 mm from costa, indusium fi rm, to 1 mm wide, hairy. Sporangial stalk with glands below the sporangium. Spores with an irregular mesh-like network of up to 10 μm high folds, fi nely papillose with spinules up to ca. 4 × 1 μm, perispore baculate, outer layer much perforated. Ecology. Epiphytic, epilithic, or less commonly terrestrial (most often at elevations over 1500m), commonly collected from mossy forests, climbing or sprawling among bryophytes and other epiphytes, or pendulous from mossy tree branches, to 600 m (Marquesas and Tahiti); or from 1000 to 3000 m (elsewhere).

Oleandra sibbaldii
Discussion. Oleandra sibbaldii is common on New Guinea, but appears to be much sparser towards the periphery of the distribution area.
Th e dark colour on the abaxial surface of the costa is often very conspicuous, extending on the stipe, thus rendering the stipe conspicuously bicolorous. 1/5-1/2 from base; lamina to 60 × 1-5.5 cm, widest in middle part, base truncate or cuneate to gradually narrowed, apex acute to narrow-acuminate, texture herbaceous, upper surface glabrous or sparsely, lower surface more densely set with usually acicular, sometimes slightly catenate hairs to c. 0.5-1.0 mm long; costa on lower surface without dark coloration, without scales. Sori close to costa or leaving a distinct 1-6 mm wide sterile zone between costa and soral zone, indusium fi rm, to 2 mm wide, hairy. Sporangial stalk without glands below the sporangium. Spores fi nely papillose and coarsely ridged, perispore baculate, outer layer not perforated. Description. Rhizome long-creeping, ca. 3 mm thick, not white waxy, sparsely branching, roots with unbranched parts; in cross-section with weakly developed sclerifi ed shealth and few scattered sclerenchyma strands, phyllopodia scattered, 3-6 cm distant, 6-7 mm long. Scales scattered, not covering the rhizome, peltate, to 5 × 0.5 mm, appressed at the base, with a narrow squarrose acumen, dark brown near attachment, lighter towards margin, margin densely set with glands and multicellular hairs terminating in a gland. Fronds monomorphic; stipes with scales as the rhizome but less dense and with short fi ne glandular hairs; stipe 2-3 mm long, without dark coloration on abaxial side, bearing short fi ne glandular hairs; lamina linear-lanceolate, 17.5-20 × 3-4 cm wide, base cuneate, apex short caudate, tips up to 1 cm long, margin undulate, weakly cartilaginous, texture papyraceous, all parts with to 0.5 mm long catenate glandular hairs, or with longer, to 1.5 mm, acicular hairs; costa abaxially without dark coloration, with hairs like the stipe and with small scales; veins terminating in a weakly developed hydathode before the margin. Sporangial stalk with glands below the sporangium. Sori in an irregular row 2.5-6 mm from the costa, indusium round-reniform, c. 0.5 mm across, fugacious at very early stage. Spores absent. Distribution. New Guinea, at 975 m. Ecology. Scandent on trunk of Sago palm in garden, or in forest. Vernacular name. Taingelem (Wapi language, Miwaute)

Oleandra undulata
Discussion. Oleandra vulpina is distinct from O. sibbaldii in the rhizome and costa scales. Rhizome scales are darker in colour with pale-coloured margin, long subulate apices, and margin strongly ciliate with glandular hairs. A similar glandular scale indument is found in the American O. articulata (Sw). C. Presl, but not in the other Southeast Asian species. Th e costa scales beneath are small and inconspicuous, narrowly lanceolate. In addition, the rhizome of O. vulpina is not glaucous. Th e indusia are very small and shrivel at a very young stage but are distinct when present and bear numerous setose hairs. Description. Rhizome creeping, 3-4 mm thick (2-3 when dry), white waxy in the older parts, with long, leafl ess parts alternating with more or less dense clusters of very short phyllopodia, usually less than 2 (-5) mm high, of which usually only 1-2 bear fronds at the same time, branches usually in opposite pairs; in cross-section with weak sclerenchyma sheath and without sclerifi ed strands, roots scattered, usually with long unbranched parts. Scales persistently covering the rhizome, peltate, 3-7 ×1-1.3 (-1.5) mm, base appressed, with dark center and lighter margin, acumen brown, usually recurved, with ciliate margin, apex twisted and with frizzly cilia. Fronds monomorphic; stipe 1-5 cm long, with dark coloration on abaxial side often distinctly bicolorous, with catenate hairs; lamina 13-45 × 2-4.5 cm, base truncate to rounded, apex often abruptly caudate, texture thin-herbaceous, translucent, both surfaces densely set with catenate hairs 0.5-1 mm long; costa on lower surface in basal half of lamina with dark coloration, with copious 2-4 mm long pale scales. Sori close to costa, indusium thin, to 1 mm wide, glabrous or hairy. Sporangial stalk without glands below the sporangium. Spores echinate and ridged, perispore solid. Distribution. Himalayas to Northern Th ailand, Yunnan and Taiwan, 1600 to 3600 m. India, Nepal, Bhutan, China (Yunnan, Taiwan), Th ailand.

Oleandra wallichii
Ecology. Mostly epiphytic, on mossy trunks, also on cliff faces or boulders. Discussion. Oleandra wallichii diff ers from O. undulata in the more wide-creeping rhizome that is often distinctly glaucous beneath and between the scales, without sclerenchyma strands; the often conspicuously bicolorous stipe, lamina with usually very distinctly apiculate apex and costa with frequent scales, sori constantly closely costal, with small indusia. 9. Oleandra werneri http://species-id.net/wiki/Oleandra_werneri Map 5 Oleandra werneri Rosenst., Repert. Spec. Nov. Regni Veg. 5: 40. 1908 Description. Rhizome with main stems creeping, scrambling or pendent, 2-3 mm thick, white waxy in the older parts, sparsely rooting, mostly terete when dry, bearing scattered short, usually less than 5 mm long phyllopodia, phyllopodia on aerial parts more closely together but not densely clustered; all parts in cross section with a peripheral sclerifi ed sheath and scattered sclerifi ed strands. Scales covering the rhizome, peltate, 3-4 × 0.5-1 mm, somewhat squarrose, with dark center and lighter margin and acumen, margin ciliate especially when young. Fronds strongly dimorphic, stipe 0.5-2.5 cm, without dark colouration, especially upwards with up to 2 mm long hairs; lamina chartaceous; fertile 27-56 × 0.5-1 (-1.7) cm, base and apex narrow, sterile 17-30 × 2.2-5.7 cm, base mostly cuneate, apex distinctly 2-3.5 cm caudate; costa and lamina on lower surface glabrous or with up to 2 mm long hairs, costa without dark colouration, like the stipe with up to 2 mm long brown scales. Sori in a single row on both sides of the costa, indusium fi rm, 1-3 mm wide, glabrous. Sporangial stalk with glands below the sporangium. Spores with coarse confl uent ridges, areolae with short pointed excrescences, perispore hollow, with internal baculae, outer layer not or hardly perforated. Distribution. Indonesia (Maluku, Papua); Papua New Guinea; Vanuatu. Ecology. Commonly epiphytic, on trunks or in crowns, less often terrestrial or on rocks, erect, scrambling or pendent, in various types of forests, most frequently in montane or mossy forests, on ridges, up to c. 2000 m.
Discussion. As in O. neriiformis, rhizome morphology is probably more complicated than can be inferred from the mostly aerial unbranching parts making up most of the collected material.
Hairiness is very variable, and while there is no sharp distinction between hairy and glabrous forms, it is noteworthy that hairy forms tend to occur at especially the Western extreme of the distribution area, with less hairy forms near the Eastern extreme and glabrous forms mostly on the mainland of New Guinea.